I have had a USPc for a while now. I shot the fullsize one fine. The compact always hit about 3-4" low. I kept shooting - tried different techniques with the trigger - holding the gun different ways, etc. Eventually, I shot on target every OTHER range trip.
At first, I thought it was the front sight that was off - but once I started doing ok every other trip, I knew itw as me. It took me 800 rounds before I got the hang of the gun. I've let other shott a few rounds too, and they tend to shoot it low.
Now, I haven't shot it in a while, so the last time I took it out, I was low again. SOmething about the gun is tricky. I've heard others say the same thing. But, it can be brought on target w/o over aiming it. It just takes time.
I shoot all my pistols with the 1st finger on my left hand on the trigger guard. For THIS gun, I have to put it UNDER the trigger guard and push up a little. That seems to work for me.